URIC ACID

Properties and Preparation

Uric acid is a colorless, odorless and tasteless solid with molecular formula C5H4N4O3. It is largely insoluble in water (60 mg/L, at 20 °C)[2]. It is soluble in 1 M NaOH (50 mg/ml)[3]. Rather than melt, it decomposes in air above 250°C. Uric acid is produced from purines by the enzyme xanthine oxidase via the purine metabolism pathway. In the majority of mammals, uric acid is further degraded to allantoin via the urate oxidase (uricase) enzyme. Allantoin is then freely excreted from the body in the urine. Humans, apes, and certain New World monkeys have higher uric acid levels compared with other mammals[4]. Commercially, uric acid has been prepared from guano, which is essentially the droppings of bats or seabirds. Large quantities of guano can be found on some islands. Uric acid can be produced via extracting guano with alkali and then precipitating with acid[5][6].

Biochem/physiol Actions

Uric acid is an insoluble catabolite produced by adenine and guanine metabolism. Accumulation of uric acid leads to gout, hyperuricemia, arthritis and renal failure. Elevated uric acid levels contributes to hypertension and pathogenesis of cardiovascular disease. Low uric acid levels associated with Parkinson′s disease and multiple sclerosis, may elicit protective functionality. High levels of uric acid in patients with chronic obstructive pulmonary disease (COPD) may serve as potential marker for diagnosis.

Safety Profile

Experimental reproductive effects. Mutation data reported. When heated to decomposition it emits toxic fumes of NOx.

Purification Methods

Crystallise uric acid from hot distilled H2O (the solubility in H2O is 1part/39,000parts at 18o and 1part/2,000parts at 100o). It is best purified by dissolving in an alkaline solution and acidifying with dilute HCl and drying it at 100o in a vacuum. [Bergmann & Dikstein J Am Chem Soc 77 691 1955, Lister Purines Part II, Fused Pyrimidines Brown Ed, Wiley-Interscience pp256-257 1971, ISBN 0-471-38205-1, Beilstein 26 H 513, 26 I 151, 26 II 293, 26 III/IV 2619.]

Introduction

Uric acid is a breakdown substance of purines which exist in body tissues and some food and drinks. Purines are a type of chemical compound in nature consisted in nucleic acids (DNA and RNA). Uric acid is created in the body via purine metabolism and circulated within the bloodstream, and it will be excreted in urine as waste. As a result, there is a certain balanced amount of uric acid in the bloodstream, which is of great importance to the functions of body[1]. Uric acid is composed in the form of urate of ammonia, and it is the primary constituent of the urine of birds and reptiles. Uric acid helps to keep the birds' weight down which is crucial for their flight. Due to its acidic properties, uric acid from birds does damage paints on cars. Insects produce uric acid during protein catabolism. In addition, uric acid helps to make butterflies iridescent. Its crystals also reflect the light produced in fireflies by bioluminescence[2].

Definition

A nitrogen compound produced from purines. In certain animals (e.g. birds and reptiles), it is the main excretory product resulting from breakdown of amino acids. In humans, uric acid crystals in the joints are the cause of gout.